Integrated switched DC-DC converters (e.g. a buck-, boost- or buck/boost-converter) mainly show two types of power losses. One type of power loss is due to charging and discharging the control gate, i.e. the gate capacitance of the power switches, e.g. power MOSFETs. The control gate typically receives an alternating control voltage that varies between the primary voltage supply level (also referred to as an input voltage or VIN) and ground. Depending on the specific type of converter and its architecture, the control gate may also receive a higher voltage. The alternating voltage levels at the gate capacitance CG cause an average DC current in the gate driving stage, flowing from the primary voltage supply VIN to ground. The power consumption POWC may be roughly approximated as:POWC=CG·f·VON2   (1)
The power consumption POWC is proportional to the switching frequency f, the gate capacitance CG and the square of the voltage level VON for turning the power switch from a high to a low level.
The second type of power losses is due to the ON-resistance of the power switches. This kind of power loss is resistive and also referred to as RDSON loss. The first order approximation of the ON-resistance RDSON is:
                    RDSON        =                              (                                                            μ                  ·                  COX                  ·                                      W                    L                                                  ⁢                                  (                                      Vgs                    -                    Vt                                    )                                            -              Vds                        )                                -            1                                              (        2        )            
Wherein COX is the gate oxide capacitance per unit control gate area, μ is the mobility of the charge carriers and W and L are the respective width and length of the control gate.
From the above equations, it becomes clear that by increasing the dimensions of the power switch, which means by increasing its width W, the ON-resistance RDSON may be lowered. However, the capacitive losses will increase, since the power consumption POWC (see Formula 1) is directly proportional to the gate capacitance that is given by:CG=COX·W·L   (3)
This means that by aiming to reduce the ON-resistance, the power consumption will increase and vice versa.
This leads to switching power converters classically exhibiting an efficiency peak for a given optimal current load. This efficiency peak is defined by the capacitive losses (i.e. by power consumption POWC) and resistive losses (i.e. RDSON) being minimal. However, when the load current is smaller or bigger than the optimal load, total losses increase and the efficiency falls rapidly. Consequently, there is only a small load current window available to the user, in which the efficiency has not fallen too much and the converter works with acceptable efficiency performance.